Equine Pastern Dermatitis (EPD), also referred to as “scratches,” “greasy heel,” or “mud fever.”

Equine pastern dermatitis is a skin disease of the lower limbs. Most commonly seen on the hind limbs, the dermatitis affects the backs of the pasterns and occasionally moves to the front of the limb. 

Signs

• Crusted lesions on the back of the pastern
• Lesions can ooze clear yellow serum
• The limb may be swollen, warm and painful on palpation
• Draft breeds and draft crosses with feathers on their distal limbs are prone to developing scratches
• Horses with white socks (ie: unpigmented skin) are also predisposed to this condition
• It is often seen in horses in muddy paddocks, rough prickly pastures and unsanitary conditions
• Generally the overall health of the horse is unaffected but severe cases can cause distal limb edema (swelling) and significant lameness
• In draft horses we sometimes see granulomatous growths of inflamed tissue at these sites 

Causes

The causative agents are usually bacteria including, Staph aureus or Dermatophilus congolensis. The exact cause of EPD can be different in each case, but the pathogenesis (which is not entirely understood) is most likely as follows: a small break in the skin allows bacteria in (unpigmented skin is more delicate, and prickly fields more abrasive) and horses in mucky conditions or with long feathers that trap dirt, heat and moisture cannot clear the infection on their own. 

Diagnosis

While the diagnosis is often made just based on clinical signs, the only way to truly know what’s causing the infection is to have your veterinarian perform a culture and in some chronic cases a biopsy is required.

Treatment

The mainstay of treatment should always be to remove all the scabs (another warm moist place where bacteria love to hide) and clean the area thoroughly and often. Clipping the hair short (with a 40# blade) will help getting down to the skin with cleaning and any topical treatments. Clipping, scrubbing and picking all the crusted areas off can be a very painful procedure and many horses have to be sedated by your vet in order to do a proper job.

Once the scabs are removed and the area is all suds up with an anti-septic solution such as 2% chlorhexidine, povidone iodine or benzoyl peroxide, I like to let the area sit for 5-10 minutes. This give the anti-septic plenty of “contact time” to kill the bacteria. After you rinse the cleanser off completely (dried soap can be irritating and itchy) the leg must be dried thoroughly (this may mean using a hair dryer on low setting for horses with feathers).

Anti-biotic creams, or sprays can be applied twice daily to aid in fighting the infection. Do not use petroleum-based ointments, instead use creams or sprays. The Vaseline like substances are water resistant and can be very difficult to completely clean off so that your scrub can reach the skin the next day. The only way to know what topical treatment will really work is to know what bacteria you are dealing with, and for that you must do a culture. Horses with lots of swelling in the lower leg or that have open fissures may benefit from a bandage but in some cases bandages will just trap in dirt and moisture. The vast majority of horses do not require systemic antibiotics but in some cases we will treat with a course of oral or injectable medications. Obviously, you must consult with your veterinarian before beginning treatments. Many horses benefit from the use of anti-inflammatories such as Bute or Banamine. Again, check with your vet for appropriate dosing.

Prognosis

Scratches can be a very frustrating disease to manage. While single episodes can be controlled and corrected, these limbs are prone to developing this dermatitis again, especially during times of the year when pastures are wet. Good hygiene and constant monitoring and cleaning and drying of the susceptible areas may prevent future outbreaks.